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ALL / Ophthalmology

Primary open-angle glaucoma: presentation and diagnosis

Primary open-angle glaucoma: presentation and diagnosis

Glaucomas are optic neuropathies associated with raised intraocular pressure (IOP). They can be classified based on whether the peripheral iris is covering the trabecular meshwork, which is important in the drainage of aqueous humour from the anterior chamber of the eye. In primary open-angle glaucoma (POAG), the iris is clear of the meshwork. The trabecular network functionally offers an increased resistance to aqueous outflow, causing increased IOP. It is now recognised that a minority of patients with raised IOP do not have glaucoma and vice versa.

Risk factors:
  • increasing age
    • affects < 1'5 in individuals under 55 years of age
    • but up to 10% over the age of 80 years
  • genetics
    • first degree relatives of an open-angle glaucoma patient have a 16% chance of developing the disease
  • Afro Caribbean ethnicity
  • myopia
  • hypertension
  • diabetes mellitus
  • corticosteroids

POAG may present insidiously and for this reason is often detected during routine optometry appointments. Features may include
  • peripheral visual field loss - nasal scotomas progressing to 'tunnel vision'
  • decreased visual acuity
  • optic disc cupping

Fundoscopy signs of POAG
  • 1. Optic disc cupping - cup-to-disc ratio >0.7 (normal = 0.4-0.7), occurs as loss of disc substance makes optic cup widen and deepen
  • 2. Optic disc pallor - indicating optic atrophy
  • 3. Bayonetting of vessels - vessels have breaks as they disappear into the deep cup and re-appear at the base
  • 4. Additional features - Cup notching (usually inferior where vessels enter disc), Disc haemorrhages

Diagnosis:
  • Case finding and provisional diagnosis is done by an optometrist
  • Referral to the ophthalmologist is done via the GP
  • Final diagnosis is done by investigations as below

Investigations:
  • automated perimetry to assess visual field
  • slit lamp examination with pupil dilatation to assess optic nerve and fundus for a baseline
  • applanation tonometry to measure IOP
  • central corneal thickness measurement
  • gonioscopy to assess peripheral anterior chamber configuration and depth
  • Assess risk of future visual impairment, using risk factors such as IOP, central corneal thickness (CCT), family history, life expectancy
+PassMedicine Notes

Glaucomas are optic neuropathies associated with raised intraocular pressure (IOP). They can be classified based on whether the peripheral iris is covering the trabecular meshwork, which is important in the drainage of aqueous humour from the anterior chamber of the eye. In primary open-angle glaucoma (POAG), the iris is clear of the meshwork. The trabecular network functionally offers an increased resistance to aqueous outflow, causing increased IOP. It is now recognised that a minority of patients with raised IOP do not have glaucoma and vice versa.

Risk factors:
  • increasing age
    • affects < 1'5 in individuals under 55 years of age
    • but up to 10% over the age of 80 years
  • genetics
    • first degree relatives of an open-angle glaucoma patient have a 16% chance of developing the disease
  • Afro Caribbean ethnicity
  • myopia
  • hypertension
  • diabetes mellitus
  • corticosteroids
POAG may present insidiously and for this reason is often detected during routine optometry appointments. Features may include
  • peripheral visual field loss - nasal scotomas progressing to 'tunnel vision'
  • decreased visual acuity
  • optic disc cupping
Fundoscopy signs of POAG
  • 1. Optic disc cupping - cup-to-disc ratio >0.7 (normal = 0.4-0.7), occurs as loss of disc substance makes optic cup widen and deepen
  • 2. Optic disc pallor - indicating optic atrophy
  • 3. Bayonetting of vessels - vessels have breaks as they disappear into the deep cup and re-appear at the base
  • 4. Additional features - Cup notching (usually inferior where vessels enter disc), Disc haemorrhages
Diagnosis:
  • Case finding and provisional diagnosis is done by an optometrist
  • Referral to the ophthalmologist is done via the GP
  • Final diagnosis is done by investigations as below
Investigations:
  • automated perimetry to assess visual field
  • slit lamp examination with pupil dilatation to assess optic nerve and fundus for a baseline
  • applanation tonometry to measure IOP
  • central corneal thickness measurement
  • gonioscopy to assess peripheral anterior chamber configuration and depth
  • Assess risk of future visual impairment, using risk factors such as IOP, central corneal thickness (CCT), family history, life expectancy


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